I'm working with a aftermarket producer of CDI units to develop a reliable, inexpensive, modern CDI to replace the heavy, ancient 33+ year old NipponsDenso CDI on the GN.

I'll be testing four different CDI units, along with tracking the advance curve and max rpm capability, and butt-dyno evaluations.

Click to expand...

That's when the name Ignitech.cz springs to mind... they have been making those for quite a few years. Additionally they're available for next to nothing from Hong Kong... maybe you want to check them out, before you invest lots of money in R&D.

I look at it this way, CDIs dating back to the mid 70s into the mid 80s are heavy, clunky, prone to vibration induced solder joint failures (somewhat common on the old Nippon-Denso Gen 1 series CDI unit). To buy a salvage CDI is a crap-shoot at best, and all you're getting is a possible copy of your problem CDI for a lot of bucks. There are more and more modern tech CDIs that are inexpensive (damn near cheap!), lightweight, readily available, durable, that can easily replace the ancient OEM units. Its not entirely hard to match CDIs for current engines to many of the older/vintage/classic bikes we enjoy to wrench and ride.

Hey Marshalltown! Been through there on a RAGBRAI ride, on my homebuilt/scratchbuilt recumbent. Nice town, like most back roads Iowa towns are.

That GN is actually a fun bike to work on and learn from. Like I have been doing for the past two years. Cheap to buy, some people nearly give them away. Simple little two-valve long stroke thumper that is cheap to buy and update. Responds well to home-tweaking, like VM36 Mikuni carb and Supertrapp pipe. Now I hope to find a bit more oommph via the ignition system.

The engine in my GN right now is one I bought for $40. Pulled the head, cleaned it up, checked the piston and rings, ring gap, bore condition, etc. Reassembled and set the valves, cam timing, etc, starts easily on the 1st kick. So now I have an extra engine to build up, bore out, shave the deck, cam, etc. I have heard of this lowly engine pushing well past 40 hp.

Since I stripped most of the street stuff off this bike, it now weighs in at only 285 pounds fueled up.

The whole salvage vs. New thing isn't a issue. I have the hondamatic version which complicates thing due to some timing magic Honda did; oem CDIs are unobtainable new and at outrageous prices used. I was about to pull the trigger on the ignitech unit, an then I saw the post I quoted. I was wondering if they were used or clones or what? The ignitech guys are pretty much the only ones with a rep that I have found.

I guess a better way to word it is, what source are you using? :)

Marshalltown isn't too bad. The riding could be a little better, but it is Iowa after all.

Wow! So glad to see this thread picked up so many riders. Looks like the 400 is the preferred rig. Sad to admit it, but I sold my gn250 to a young guy last summer, I caught a glimpse of him with a friend/passenger on one of my local back roads, brought a smile... She's still out there! Occasionally I miss the GN, but my DR650 is treating me well too, so no complaints.

Speedshop any update on the cdi unit i have a couple motors sitting around and in need of cdi's. I dont want to shell out the coin for a used one or a NOS which are ridiculous, also 12v conversion sounds great to me.

Hello there,
Iris, my wife, started riding on a GN 400 in 1981 and since that time, we always had one or two of them running. In the meantime we got a compilation of about 3 complete bikes, one more could be built from all the parts lying around in our barn and there are parts of about 3 more incomplete bikes. Sadly, usually the parts you need are shot on the wrecked bikes you get offered.
I have to admit, that the GNs slipped a bit out of our focus since I got my 1988 Suzuki DR Big 750 in 2008 and Iris her 2004 Ducati Monster 800 this spring. But they're not and never will be forgotten, especially, as they saved our motorcycling souls at times when money was too tight to run and repair our bigger or more complicated bikes (Triumph Tiger Trail, Triumph Bonneville, the already mentioned Big 750, 250 off-road MZ, 175 off-road Hercules Sachs).
We always lookeed at the GN as being some kind of modern BSA Gold Star or something like that, light, powerfull enough, good handling and ... reliable! I think, all in all we put about 150. - 200.000 kms on them. Iris still likes her in nearly standard trim, which is a bit too cramped in seat-position for me. So I put on a super-bike handle-bar and some BMW GS foot-rests (a bit narrower and higher-positioned than the original ones) on mine. So I'm no more pushed towards the small step in the seat (we only have TD-models, the L-model has a highly stepped seat, a buckhorn handle-bar and cast wheels) and lean-angle on the right side now is limited by the exhaust-clamp that I'm used to grind off. On the left side, the lean-angle is limited by the poor tyre-performance.
That's were my plans of beefing up the little thing come in. I'd like to put a 17-inch-rim on the back to get a better tyre-choice. Brakes are fine so far, there's no big need for changes. I'm planning to put a rear-swinging-arm from an RM- or PE-model in it. They're made of alloy and they're a bit longer. The resulting plus of wheel-base might compensate for the lift of the back by the bigger wheel. I don't, but Iris experiences a bit of a wobble in the bars with the slightly fatter mm- compaired to the original inch-tyre-sizes and the slightly longer Koni rear-shocks when doing 100 km/h or more. I address this to the some 40 kgs I do weigh more than her because I hadn't this effect on my bike with about the same set-up. And I would like to make mine look more like a Super Moto or a Street-Scrambler/-Tracker. So that it looks the way it is ridden ...
Kind regards, Bambi

To royota and speedshop; so far my GN400 is running fine using:
Honda CH250 original or clone CDI
Honda CH250 original or clone coil/plug lead

It uses the trigger signal from the 10 degree BTDC coil only. The other trigger coil is not used at all. Starts easy, idles fine, gotten the bike over 6,000 rpm on it. The Honda parts are plentiful, reliable and inexpensive. But to make this work you really need to match the coil to the CDI. Before I was running the Honda CDI with the stock Suzuki coil at it sputtered to get over 4500 rpm. Now over 6000 rpm is working good.

I still suspect though, that the CH250 CDI may have too gradual of an advance curve for the timing on the GN400. Stock timing advance on the GN400 is a curved ramp up from 2000 RPM up to max advance at 4500, then the curve flat lines to redline.

Stock timing advance on the CH250 is a linear ramp, up from 1500 RPM up to max advance at 7000 RPM and redline. The CH250 service manual says to check for max timing advance (F mark on the rotor) at 7,000 RPM. Maybe a scooter needs such gradual advance for easy sedate riding. Don't wanna scare grandma on the scooter with too much advance!

So, that is far too gradual an advance curve for good performance on a big bore single. So I am testing a switch wired between the stock GN 10 degree pulser coil and the 35 degree pulser coil. Switched to the 10 degree pulser coil gives me real easy starting and a smooth idle. Then switching to the 35 degree pulser coil should give much better performance. I do recall, last year I did get the GN started when I had it wired to the 35 degree pulser coil and it ran strong!! My buddy popped a wheelie on it real easy, said "THAT never happened before!"

Hoping to resurrect this old thread; have owned hundreds of bikes in my 49 years, but am picking up a GN400 this afternoon ... haven't even seen the bike, seller is delivering for me. Anxious to get some seat time on it; supposedly it runs pretty well, but has no title. Anyone out there have a titled frame for sale?